1. Technical Field
The present invention relates generally to database programs implemented on data processing systems. Specifically, the present invention identifies changes made to rows contained in a database by analyzing the database management system's transaction log data.
2. Description of the Related Art
Large electronic databases have become common-place items on many of today's large computer systems. These electronic databases, and the database management programs which manipulate and make accessible the data in the database, allow vast amounts of information to be stored in an orderly, easily retrievable manner. Most large corporations now rely heavily on the information contained in these electronic databases. However, computer systems and electronic data systems still experience unexpected failures which can result in the loss of some or all of the data contained in an electronic database.
One way to combat these unexpected failures is to periodically make backup copies of the database. However, for large databases, this can be a time consuming process and can only be done infrequently. To supplement these backup copies of the database, many database management programs maintain a record of the changes that are made to the database. The information describing the changes made to a database is often known as transaction log data. This log data can be kept in files or other virtual storage devices known as transaction logs. Transaction logs are useful in recovering lost data because they often contain all of the changes that have been made to a database from the point in time a backup was made to the present. For example, assume that a backup of a database is taken on a Monday and that a transaction log containing all of the changes that were made to the database from that point on is maintained. If the database “crashes” or becomes unusable on Friday, the changes stored in the transaction log from the time the backup was taken on Monday until the time the database became unusable can be implemented to the Monday version of the database to restore the database.
Although the transaction log contains much useful information, tools which make use of this information are few in number. For instance, sometimes the entire database will not crash, but a portion of the database will be found to contain incorrect information. This incorrect information could be the result of a failure of the computer system's hardware or software, or, due to human error, the information could simply have been incorrectly entered into the database. Normally, when such an error is discovered, the entire database has to be brought back to the last known correct state. Using the example discussed above, suppose an error is discovered in the database on Thursday, and the backup of the database taken on Monday is known to be a good copy, without the error. In order to correct the error, the Monday backup copy of the database is used in place of the copy of the database which contains the error. This results in restoring the database to a known, valid state. However, all of the entries made to the database from Monday to Thursday are lost and have to be reentered.
Thus, a method which utilizes transaction log data and allows for the inspection of the changes made to individual rows would be useful. Such a method would examine the transaction log data and recreate rows in the database as they existed before and after a change. Displaying the rows in such a manner would put the changes described in the transaction log data in context and would allow a user to more fully utilize the contents of the transaction log data.